Bonding structure of valve seat and method of making the same

BACKGROUND OF THE INVENTION

The present invention relates to a bonding structure of a valve seat and more particularly to structure and method for bonding the valve seat insert to a head by pressure welding such that the head physically secures the valve seat insert for forming the valve seat for an internal combustion engine.

In a general valve for an internal combustion engine, an annular valve seat insert is made of a sintered ferroalloy, and the intake and exhaust port openings of a cylinder head are made of an aluminum alloy. The valve seat insert is bonded to the cylinder head by heating and pressing the valve seat insert into a recess formed at each port opening.

In this heating and pressing process, the annular valve seat insert is required to be relatively thick to counter internal stress generated due to shrink. Therefore, bonding the valve seat insert by welding or others, which generates less internal stress, has been tried such that the valve seat insert becomes relatively thin. Japanese Unexamined Patent Publication No. 11-50823 discloses that the valve seat insert is bonded by friction welding, which applies an ultrasonic vibration. Also, Japanese Unexamined Patent Publication No. 8-296417 and No. 2000-263241 disclose that the valve seat insert is bonded by electric resistance welding.

By utilizing any way, since the cylinder head made of an aluminum alloy and the valve seat insert made of a sintered ferroalloy, which are different materials, are bonded, a weak intermetallic compound and an oxidized layer are produced at a transition region between the cylinder head and the valve seat insert, thus weakening the bonding strength therebetween. Therefore, to increase the bonding strength, the valve seat insert itself may contain a diffusible material, which is diffusible to an aluminum alloy, or may includes a layer of the diffusible material, or solder may be interposed between the cylinder head and the valve seat insert.

In the above-mentioned bonding structure of the valve seat bonded by friction welding or by electric resistance welding ensures degree of freedom to design, for example, thickness of the valve seat insert may be relatively thin. However, the structure does not completely retard the valve seat insert from falling out.

SUMMARY OF THE INVENTION

The present invention addresses the above-mentioned problems traceable to the bonding strength between a head and a valve seat insert by improving a bonding structure such that the head physically secures the valve seat insert.

According to the present invention, a bonding structure of a valve seat has a port opening of a metallic head and an annular metallic valve seat insert. The valve seat insert includes an outer reduced diameter surface on its outer circumference. The material of the valve seat insert is harder than that of the head. The head plastically deforms upon pressing the valve seat insert toward the head. The deformed head occupies any gap around the outer reduced diameter surface.

The present invention also provides a method of making a valve seat. The method includes pressing a valve seat insert, which provides an outer reduced diameter surface, toward a head, rotating the valve seat insert while pressing the valve seat insert, and cooling the valve seat insert and the head.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a valve seat insert and a cylinder head, which are assembled to a valve mechanism for an internal combustion engine after bonding according to a first embodiment of the present invention;

FIG. 2 is an enlarged partial cross-sectional view of a valve seat insert and a cylinder head before bonding according to the first embodiment of the present invention;

FIGS. 3<i>a </i>through <b>3</b><i>f </i>are partial cross-sectional views of a procedure for bonding a valve seat insert to a cylinder head according to the first embodiment of the present invention;

FIG. 4 is a cross-sectional view of a valve seat insert and a cylinder head before bonding according to a second embodiment of the present invention;

FIGS. 5<i>a </i>through <b>5</b><i>e </i>are cross-sectional views of a procedure for bonding a valve seat insert to a cylinder head according to the second embodiment of the present invention;

FIG. 6 is a cross-sectional view of a valve seat insert and a cylinder head before bonding according to a third embodiment of the present invention;

FIG. 7 is a cross-sectional view of a valve seat insert and a cylinder head before bonding according to a fourth embodiment of the present invention;

FIG. 8 is a cross-sectional view of a valve seat insert and a cylinder head before bonding according to a fifth embodiment of the present invention;

FIGS. 9<i>a </i>through <b>9</b><i>c </i>are cross-sectional views of a valve seat insert and a cylinder head before bonding, and a procedure for bonding the valve seat insert to the cylinder head according to a sixth embodiment of the present invention; and

FIGS. 10<i>a </i>through <b>10</b><i>c </i>are cross-sectional views of a valve seat insert and a cylinder head before bonding, and a procedure for bonding the valve seat insert to the cylinder head according to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will now be described with reference to FIGS. 1 through 3.

As shown in FIG. 1, a bonding structure <b>1</b> of a valve seat is constituted of a cylinder head <b>5</b> and an a valve seat insert <b>6</b>. A recess <b>12</b> is formed at the end of the port opening <b>11</b> of the cylinder head <b>5</b> by pressing the valve seat insert <b>6</b> toward the cylinder head <b>5</b>. The valve seat insert <b>6</b>, which is annular in shape, is bonded to the cylinder head <b>5</b> so as to be fitted into the recess <b>12</b>. An inclined surface <b>23</b> as an outer reduced diameter surface, which gradually reduces its diameter toward the opposite side of the cylinder head <b>5</b>, resides on an outer circumference of the valve seat insert <b>6</b>. A deformed metal <b>14</b>, the cross section of which is wedge-shaped, occupies any gap around the inclined surface <b>23</b>, and is solidified. The deformed metal is softened by increasing its temperature, and is fluidized. An inner periphery of the valve seat insert <b>6</b> facing a combustion chamber, or the opposite side of the cylinder head <b>5</b>, is machined to a tapered surface with an angle of 45 degrees relative to the central axis of the port opening <b>11</b>, thus forming a valve seat <b>15</b>. In the bonding structure <b>1</b> of the valve seat, the valve body <b>7</b> is disposed on the valve seat <b>15</b> so as to move up and down relative to the valve seat <b>15</b> of the valve seat insert <b>6</b>. Thereby, a valve <b>2</b> for an internal combustion engine is constructed.

FIG. 2 shows a valve seat insert and a cylinder head before bonding. The cylinder head <b>5</b> is made of a metal such as an aluminum alloy, for example, Al—Si. The valve seat insert <b>6</b> is made of a metal such as a ferroalloy or a sinter of those alloys. The material of the valve seat insert <b>6</b> is harder than that of the cylinder head <b>5</b>.

The recess <b>21</b> of the cylinder head <b>5</b> is constituted of a first recess <b>211</b>, the diameter D<b>2</b> of which is larger than the diameter D<b>1</b> of the port opening <b>11</b>, a second recess <b>212</b>, the diameter D<b>3</b> of which is much larger than the diameter D<b>2</b> of the first recess <b>211</b>, and a step <b>213</b> between the first recess <b>211</b> and the second recess <b>212</b>.

The valve seat insert <b>6</b> is annular in shape, and has an inside diameter of D<b>5</b>, an outermost outside diameter of D<b>7</b> and a thickness of H<b>5</b>. The valve seat insert <b>6</b> provides a truncated cone-shaped first inclined surface <b>23</b>, or an outer reduced diameter surface, which is positioned farther from the cylinder head <b>5</b> than an outermost point <b>22</b> of the valve seat insert <b>6</b>. The valve seat insert <b>6</b> also provides a truncated cone-shaped second inclined surface <b>24</b>, which is positioned closer to the cylinder head <b>5</b> than the outermost point <b>22</b>. Since the deformed metal shaped into a wedge occupies the gap around the first inclined surface <b>23</b>, the angle α of the first inclined surface <b>23</b> is preferably 10 to 15 degrees. Also, since the second inclined surface <b>24</b> forces the deformed metal out to the first inclined surface <b>23</b>, the angle β of the second inclined surface <b>24</b> is preferably 45 degrees or below.

The outermost outside diameter D<b>7</b> of the vale seat insert <b>6</b> is preferably a little smaller than the diameter D<b>3</b> of the second recess <b>212</b> so that the deformed metal smoothly flows onto the first inclined surface <b>23</b>. In the valve seat insert <b>6</b>, and the bottom diameter D<b>6</b> of an end surface facing the cylinder head <b>5</b> is preferably a little smaller than the diameter D<b>2</b> of the first recess <b>211</b> so that the second inclined surface <b>24</b> abuts against the edge of the step <b>213</b>. The diameter D<b>5</b> of the valve seat insert <b>6</b> is preferably a little smaller than the diameter D<b>1</b> of the port opening <b>11</b> so as to guide a burr of the deformed metal. The thickness H<b>5</b> of the valve seat insert <b>6</b> is preferably a little larger than the depth H<b>1</b> of the recess <b>21</b> so as to save a leave for upsetting upon pressing.

FIG. 3 shows a procedure for bonding a valve seat insert <b>6</b> and a cylinder head <b>5</b>. The valve seat insert <b>6</b> is pressed toward the cylinder head <b>5</b> with its rotated. As shown in FIG. 3<i>a</i>, the valve seat insert <b>6</b> is fitted into the recess <b>21</b> of the cylinder head <b>5</b>. The edge of the step <b>213</b> abuts against the second inclined surface <b>24</b>. In such a state, the valve seat insert <b>6</b> is pressed against the cylinder head <b>5</b> by applying predetermined pressure P to the valve seat insert <b>6</b>. As shown in FIG. 3<i>b</i>, as the valve seat insert <b>6</b> is pressed with its rotated, the edge of the step <b>213</b> is deformed, and flows along the second inclined surface <b>24</b>.

As shown in FIG. 3<i>c</i>, the deformed metal forced out to the outermost point <b>22</b> crosses the outermost point <b>22</b>, and flows along the first inclined surface <b>23</b> toward the opposite side of the cylinder head <b>5</b>. As shown in FIG. 3<i>d</i>, the end of the valve seat insert <b>6</b> facing the cylinder head <b>5</b> abuts against the bottom of the first recess <b>211</b> of the cylinder head <b>5</b>, and continues to be pressed against the cylinder head <b>5</b> with its rotated until the deformed metal occupies any gap around the first recess <b>211</b>. As shown in FIG. 3<i>e</i>, the valve seat insert <b>6</b> is stopped rotating, and is upset by pressing. As the cylinder head <b>5</b> abutting against the valve seat insert <b>6</b> is deformed, the valve seat insert <b>6</b> is further pushed in. The deformed metal is forced out onto the first inclined surface <b>23</b> and to the port opening <b>11</b>.

Cooled in a state of FIG. 3<i>e</i>, the wedge-shaped deformed metal <b>14</b> around the first inclined surface <b>23</b> of the valve seat insert <b>6</b> is solidified. The solidified deformed metal <b>14</b> occupies any gap around the valve seat insert <b>6</b>, and physically secures the valve seat insert <b>6</b> to the cylinder head <b>5</b>. As shown in FIG. 3<i>f</i>, the bonding structure <b>1</b> of the valve seat with designed dimensions is made by the following steps: removing a burr of the deformed metal <b>14</b> by machining the inner surface of the valve seat insert <b>6</b> and the distal end of the valve seat insert relative to the cylinder head <b>5</b>; and forming the valve seat <b>15</b> by machining the edge between the distal end and the inner surface.

In FIG. 3<i>f</i>, if the deformed metal <b>14</b> does not occupy the gap around the first inclined surface <b>13</b> enough, the deformed metal <b>14</b> after removing the burr is defectively formed with some gaps. Therefore, the valve seat <b>15</b> firmly secured is selected based on its appearance test.

A second embodiment of the present invention will now be described with reference to FIGS. 4 and 5.

A cylinder head <b>5</b>A provides a recess <b>31</b>, which is D<b>13</b> in diameter and H<b>11</b> in depth, and the diameter D<b>13</b> is larger than the diameter D<b>11</b> of the port opening <b>11</b>. A valve seat insert <b>6</b>A is annular in shape, and is D<b>15</b> in inside diameter, D<b>17</b> in outermost outside diameter and H<b>15</b> in thickness. The valve seat insert <b>6</b>A also provides a truncated cone-shaped inclined surface <b>33</b> or an outer reduced diameter surface on its outer circumference, the angle of the inclined surface <b>33</b> is α degree perpendicular to the central axis of the port opening <b>11</b>. The inclined surface <b>33</b> is positioned farther from the cylinder head <b>5</b>A than an outermost point <b>32</b> of the valve seat insert <b>6</b>A.

The outermost outside diameter D<b>17</b> of the vale seat insert <b>6</b>A is preferably a little smaller than the diameter D<b>13</b> of the recess <b>31</b> so that the deformed metal smoothly flows onto the inclined surface <b>33</b>. The diameter D<b>15</b> of the valve seat insert <b>6</b>A is preferably a little smaller than the diameter D<b>11</b> of the port opening <b>11</b> so as to guide a burr of the deformed metal. The thickness H<b>1</b><b>5</b> of the valve seat insert <b>6</b>A is preferably a little larger than the depth H<b>11</b> of the recess <b>31</b> so as to save a leave for upsetting upon pressing.

FIG. 5 shows a procedure for bonding a valve seat insert <b>6</b>A to a cylinder head <b>5</b>A. The valve seat insert <b>6</b>A is pressed toward the cylinder head <b>5</b>A with its rotated. As shown in FIG. 5<i>a</i>, the valve seat insert <b>6</b>A is fitted into the recess <b>31</b> of the cylinder head <b>5</b>A. The end of the valve seat insert <b>6</b>A abuts against the bottom of the recess <b>31</b>. In such a state, the valve seat insert <b>6</b>A is pressed against the cylinder head <b>5</b>A by applying predetermined pressure P to the valve seat insert <b>6</b>A. As shown in FIG. 5<i>b</i>, as the valve seat insert <b>6</b>A is pressed with its rotated, the bottom of the recess <b>31</b> is deformed, and the deformed metal crosses the outermost point <b>22</b>, then flows along the inclined surface <b>33</b>.

As shown in FIG. 5<i>c</i>, the valve seat insert <b>6</b>A is stopped rotating, and continues to be pressed. Since the bottom of the cylinder head <b>5</b>A abutting against the valve seat insert <b>6</b>A is deformed, the valve seat insert <b>6</b>A is further pushed in. The deformed metal is forced out onto the inclined surface <b>33</b>, and is shaped into a wedge. As shown in FIG. 5<i>d</i>, the wedge-shaped deformed metal <b>34</b> is solidified by cooling, and is united with a base metal of the cylinder head <b>5</b>A. The wedge-shaped deformed metal <b>34</b> occupies any gap around the valve seat insert <b>6</b>A, and physically secures the valve seat insert <b>6</b>A to the cylinder head <b>5</b>A. As shown in FIG. 5<i>e</i>, the bonding structure <b>1</b>A of the valve seat with designed dimensions is made by the following steps: removing a burr of the deformed metal <b>34</b> by machining the inner surface of the valve seat insert <b>6</b>A and the distal end of the valve seat insert <b>6</b>A relative to the cylinder head <b>5</b>A; and forming the valve seat <b>35</b> by machining the edge between the distal end and the inner surface.

In FIG. 5<i>e</i>, if the deformed metal <b>34</b> does not occupy the gap around the inclined surface <b>33</b> enough, the deformed metal <b>34</b> is defectively formed with some gaps after removing the burr. Therefore, the firmly secured valve seat <b>35</b> is is selected based on its appearance test.

A third embodiment of the present invention will now be described with reference to FIG. <b>6</b>.

As shown in FIG. 6, the shape of the cylinder head <b>5</b>B is the same as that in the first embodiment. A valve seat insert <b>6</b>B provides an inclined surface <b>43</b> and an outer reduced diameter surface <b>42</b> on its outer circumference. The inclined surface <b>43</b> is positioned closer to the cylinder head <b>5</b>B than an outermost surface <b>41</b> of the valve seat insert <b>6</b>B, as well as that in the first embodiment. The outer reduced diameter surface <b>42</b>, which is semicircular in shape, is positioned farther from the cylinder head <b>5</b>B than the outermost surface <b>41</b>. The valve seat insert <b>6</b>B also provides a cylindrical surface <b>44</b>, the diameter of which is smaller than the diameter of the outermost surface <b>41</b>, on its outer circumference. The cylindrical surface <b>44</b> is positioned farther from the cylinder head <b>5</b>B than the outer reduced diameter surface <b>42</b>. A clearance ε is set between the cylindrical surface <b>44</b> and the outermost surface <b>41</b>.

As well as those in the first embodiment, the deformed metal flows along the inclined surface <b>43</b>, and crosses the outmost surface <b>41</b>, then occupies any gap around the outer reduced diameter surface <b>42</b>. The deformed metal occupying the gap around the outer reduced diameter surface <b>42</b> is solidified, and is united with a base metal of the cylinder head <b>5</b>B. Also, since the deformed metal occupying the gap around the outer reduced diameter surface <b>42</b> is forced out through the clearance ε, and is exposed outside. Therefore, the outer reduced diameter surface <b>42</b> filled with the deformed metal is checked based on its appearance.

A fourth embodiment of the present invention will now be described with reference to FIG. <b>7</b>.

As shown in FIG. 7, the shape of the cylinder head <b>5</b>C is the same as that in the first embodiment. A valve seat insert <b>6</b>C provides an inclined surface <b>53</b> and an outer reduced diameter surface <b>52</b> on its outer circumference. The inclined surface <b>53</b> is positioned closer to the cylinder head <b>5</b>C than an outermost point <b>51</b> of the valve seat insert <b>6</b>C, as well as that in the first embodiment. The outer reduced diameter surface <b>52</b>, which is a catch, is positioned farther from the cylinder head <b>5</b>C than the outermost point <b>51</b>. The valve seat insert <b>6</b>C also provides another peak point <b>54</b>, the diameter of which is smaller than the diameter of the outermost point <b>51</b>, on its outer circumference. The peak point <b>54</b> is positioned farther from the cylinder head <b>5</b>C than the outer reduced diameter surface <b>52</b>. A clearance ε is set between the peak point <b>54</b> and the outermost point <b>51</b>.

As well as those in the first embodiment, the deformed metal flows along the inclined surface <b>53</b>, and crosses the outmost point <b>51</b>, then occupies any gap around the outer reduced diameter surface <b>52</b> as a catch. The deformed metal occupying the gap around the outer reduced diameter surface <b>52</b> is solidified, and is united with a base metal of the cylinder head <b>5</b>C. Also, since the deformed metal occupying the gap around the outer reduced diameter surface <b>52</b> is forced out through the clearance ε, the outer reduced diameter surface <b>52</b> filled with the deformed metal is checked based on its appearance.

A fifth embodiment of the present invention will now be described with reference to FIG. <b>8</b>.

As shown in FIG. 8, the shape of the cylinder head <b>5</b>D is the same as that in the first embodiment except that the second recess is a truncated cone-shaped recess <b>60</b>. A valve seat insert <b>6</b>D provides a first inclined surface <b>61</b> and a second inclined surface <b>62</b> on its outer circumference. The first and second inclined surfaces <b>61</b>, <b>62</b>, which are truncated cone-shaped, are positioned on the outer circumference of the valve seat insert <b>6</b>D. The valve seat insert <b>6</b>D also provides an outer reduced diameter surface <b>63</b> as a catch, which is an annular groove. The outer reduced diameter surface <b>63</b> is positioned between the first and second inclined surfaces <b>61</b>, <b>62</b>, and provides a step for inhibiting the valve seat insert <b>6</b>D from falling out. A clearance ε is set between the first and second inclined surfaces <b>61</b>, <b>62</b>.

As well as those in the first embodiment, the deformed metal flows along the inclined surface <b>61</b>, and occupies any gap around the outer reduced diameter surface <b>63</b>. The deformed metal occupying the gap around the outer reduced diameter surface <b>63</b> is solidified, and is united with a base metal of the cylinder head <b>5</b>D. Also, since the deformed metal occupying the gap around the outer reduced diameter surface <b>63</b> is forced out through the clearance ε, the outer reduced diameter surface <b>63</b> filled with the deformed metal is checked based on its appearance.

A sixth embodiment of the present invention will now be described with reference to FIGS. 9<i>a </i>through <b>9</b><i>c. </i>

As shown in FIG. 9<i>a</i>, the cylinder head <b>5</b>E remains its shape after casting without machining for forming a recess at the port opening <b>11</b>. A valve seat insert <b>6</b>E provides a first inclined surface <b>73</b> as an outer reduced diameter surface and a second inclined surface <b>74</b> on its outer circumference. The first inclined surface <b>73</b>, which is truncated cone-shaped, is positioned farther from the cylinder head <b>5</b>E than an outermost point <b>72</b> of the valve seat insert <b>6</b>E. The second inclined surface <b>74</b>, which is truncated cone-shaped, is positioned closer to the cylinder head <b>5</b>E than the outermost point <b>72</b>. The valve seat insert <b>6</b>E also provides a third inclined surface <b>75</b> on its inner circumference, and has an edge <b>76</b> on one end.

In FIG. 9<i>b</i>, as the valve seat insert <b>6</b>E is pressed toward the cylinder head <b>5</b>E with its rotated, the port opening <b>11</b> and the end surface <b>13</b> of the cylinder head <b>5</b>E are deformed, and the deformed metal are forced out. Due to the forced out deformed metal, the deformed metal occupies any gap around the first inclined surface <b>73</b> enough. In FIG. 9<i>c</i>, a valve seat <b>77</b><i>c </i>is formed by the following steps: forming the port opening <b>11</b> by machining the inner surface <b>11</b><i>a </i>of the cylinder head <b>5</b>E and the inner surface <b>77</b><i>a </i>of the valve seat insert <b>6</b>E together; forming a plate-shaped end by machining the end <b>11</b><i>b </i>of the cylinder head <b>5</b>E and the end <b>77</b><i>b </i>of the valve seat insert <b>77</b><i>b </i>together; and machining the edge between the inner surface <b>77</b><i>a </i>and the end <b>77</b><i>b. </i>

In FIG. 9<i>c</i>, the deformed metal occupies the gap around the first inclined surface <b>73</b> enough, and the first inclined surface <b>73</b> filled with the deformed metal is checked after machining based on its appearance.

A seventh embodiment of the present invention will now be described with reference to FIGS. 10<i>a </i>through <b>10</b><i>c. </i>

In FIG. 10<i>a</i>, the cylinder head <b>5</b>F provides a recess <b>81</b> at the end of the port opening <b>11</b>, and the recess <b>81</b> is constituted of a first recess <b>811</b> and a second recess <b>812</b>. A valve seat insert <b>6</b>F provides a first inclined surface <b>83</b> as an outer reduced diameter surface and a second inclined surface <b>84</b>, on its outer circumference. The first inclined surface <b>83</b>, which is truncated cone-shaped, is positioned farther from the cylinder head <b>5</b>F than a peak point <b>82</b> of the valve seat insert <b>6</b>F. The second inclined surface <b>84</b>, which is truncated cone-shaped, is positioned closer to the cylinder head <b>5</b>F than the peak point <b>82</b>. The valve seat insert <b>6</b>F also provides a cap portion <b>85</b> and a step <b>85</b><i>a</i>. The cap portion <b>85</b> is positioned at the distal end of the valve seat insert <b>6</b>F relative to the cylinder head <b>5</b>F. The step <b>85</b><i>a </i>is positioned between the first inclined surface <b>83</b> and the cap portion <b>85</b>. The diameter of the peak point <b>82</b> is substantially equal to the diameter of the second recess <b>812</b>. The diameter of the cap portion <b>85</b> is larger than the diameter of the peak point <b>82</b>, A clearance δ is set between the cap portion <b>85</b> and the peak point <b>82</b>.

In FIG. 10<i>b</i>, as the valve seat insert <b>6</b>F is pressed toward the cylinder head <b>5</b>F with its rotated, the deformed metal flows onto the first inclined surface <b>83</b> of the valve seat insert <b>6</b>F, and is blocked by the cap portion, thus promoting the deformed metal occupies any gap around the first inclined surface <b>83</b>.

In FIG. 10<i>c</i>, a valve seat <b>87</b><i>c </i>is formed by the following steps: forming a plate-shaped end by machining the end <b>11</b><i>b </i>of the cylinder head <b>5</b>F and the end is <b>87</b><i>b </i>of the valve seat insert <b>6</b>F together; simultaneously removing a portion corresponding to the cap portion <b>85</b> of the valve seat insert <b>6</b>F; and machining the edge between the inner surface of the valve seat insert <b>6</b>F and the end <b>87</b><i>b. </i>

In FIG. 10<i>c</i>, the deformed metal occupies the gap around the first inclined surface <b>83</b> enough, and the first inclined surface <b>83</b> filled with the deformed metal is checked after machining based on its appearance.

According to the embodiments described above, the following advantageous effects are obtained.

(1) In the first through seventh embodiments, the deformed metal made of the cylinder heads occupy any gap around the inclined surfaces <b>23</b>, <b>33</b>, <b>73</b>, <b>83</b> as an outer reduced diameter surface, and around the outer reduced diameter surfaces <b>42</b>, <b>52</b>, <b>63</b> as a catch, and are united with the base metals of the cylinder heads. Thereby, the valve seat inserts are physically secured to the cylinder heads. Accordingly, a bonding structure by friction welding, which has been a difficult task in its bonding strength, is applied. As the bonding structure physically secured by friction welding is applied, limitation on materials adopted to the bonding surface of the valve seat inserts may be reduced. Furthermore, the valve seat inserts may be thinner as compared with those made by pressure welding, and design requirements about dimensions and materials of the valve seat inserts may be improved.

(2) In the first through seventh embodiments, since the deformed metal occupying the gaps around the inclined surfaces <b>23</b>, <b>33</b>, <b>73</b>, <b>83</b> as an outer reduced diameter surface, or the outer reduced diameter surfaces <b>42</b>, <b>52</b>, <b>63</b> as a catch, flow along the inclined surfaces <b>23</b>, <b>33</b>, <b>73</b>, <b>83</b>, or flow through the clearance ε, and are exposed outside, bonding including physical secureness is checked based on their appearances. Thereby, all of the valve seats are easily checked, and the firmly secured valve seats may only be products.

(3) In the first, second, sixth and seventh embodiments, since the outer reduced diameter surfaces are the inclined surfaces <b>23</b>, <b>33</b>, <b>73</b>, <b>83</b>, the deformed metal occupying the gaps around the inclined surfaces <b>23</b>, <b>33</b>, <b>73</b>, <b>83</b> is wedge-shaped. Thereby, the valve seat inserts are physically secured to the cylinder heads.

(4) In the first, third through fifth embodiments, the valve seat inserts provide the inclined surfaces <b>24</b>, <b>43</b>, <b>53</b>, <b>61</b> on their outer circumference. The inclined surfaces <b>24</b>, <b>43</b>, <b>53</b>, <b>61</b> abut against steps, one of which is the step <b>213</b> shown in FIG. 2, and the cylinder heads are deformed. Thereby, thrust force upon starting friction welding is reduced. Also, the deformed metal flows along the inclined surfaces <b>24</b>, <b>43</b>, <b>53</b>, <b>61</b>, then to the inclined surface <b>23</b> as an outer reduced diameter surface, or the outer reduced diameter surfaces <b>42</b>, <b>52</b>, <b>63</b> as a catch. Thereby, the deformed metal surely occupies the gaps around the valve seat inserts.

(5) In the first and second embodiments, since the shapes of the outer circumference of the valve seat inserts are constituted of two inclined surfaces or one inclined surface, the valve seat inserts <b>6</b>, <b>6</b>A made of a metal such as a sintered metal is easily formed. Particularly, the shape of the valve seat insert <b>6</b>A in the second embodiment only provides one inclined surface on its outer circumference so that the inclined surface is easily formed.

(6) In the first through seventh embodiments, any cylinder heads are deformed due to friction welding. Factors such as speed, pressure and the amount of upsetting for friction welding may be controlled easier than that of current control for electric resistance welding, with a consequence of high reproducibility, stabilized quality and production equipment with, a simple structure.

(7) In the first through seventh embodiments, as the cylinder heads are deformed due to friction welding, part of the cylinder heads abutting against the valve seat inserts are effected by puddling upon welding. Thereby, toughness of the cylinder heads may be improved. Consequently, mechanical characteristic of the base metal supporting the valve seat inserts improves, and durability of the valve seat inserts against a shock generated upon opening and closing valves improves as a whole. Particularly, in the valve for an internal combustion engine, since a shock upon opening and closing the valve is large, disposing tough materials around the valve seat inserts is preferable.

(8) In the fourth and fifth embodiments, the openings of the valve seat inserts <b>6</b>C, <b>6</b>D may increase their diameter toward their one end, while the outer circumferences of the valve seat inserts <b>6</b>C, <b>6</b>D may increase their diameter toward their one end. In such a state, since the valve seat inserts <b>6</b>C, <b>6</b>D provide the outer reduced diameter surfaces <b>52</b>, <b>63</b> as a catch on their outer circumferences, the valve seat inserts <b>6</b>C, <b>6</b>D may physically be secured to the cylinder heads <b>5</b>C, <b>5</b>D. Since the deformed metal occupying the gaps around the outer reduced diameter surfaces <b>52</b>, <b>63</b> is exposed outside, the outer reduced diameter surfaces <b>52</b>, <b>63</b> filled with the deformed metal are checked based on their appearances.

(9) In the sixth embodiment, since one end of the valve seat insert <b>6</b>E provides the edge <b>76</b>, initial thrust force for deforming the cylinder head <b>5</b>E may be reduced upon pressing the valve seat insert <b>6</b>E against the end surface <b>13</b> of the cylinder head <b>5</b>E synchronously with rotating the valve seat insert <b>6</b>E. Thereby, a general numerically-controlled machine or an NC machine may achieve friction welding without using a special friction welding machine. Also, since the valve seat insert <b>6</b>E is pressed into the port opening <b>11</b> of the cylinder head <b>5</b>E without forming a recess around the end of the port opening <b>11</b>, a relatively large amount of cylinder head <b>5</b>E is deformed. Thereby, the deformed metal occupies any gap around the first inclined surface <b>73</b> enough, and is shaped into a wedge, then solidifies.

(10) In the seventh embodiment, the valve seat insert <b>6</b>F provides the cap portion <b>85</b> on its distal end relative to the cylinder head <b>5</b>F. Thereby, the cap portion <b>85</b> dams off the deformed metal flowed onto the first inclined surface <b>83</b>, and the deformed metal occupies any gap around the first inclined surface <b>83</b> enough, and is shaped into a wedge, then solidifies. The wedge-shaped deformed metal occupying the gap around the first inclined surface <b>83</b> is exposed outside by removing the cap portion <b>85</b> by machining. Therefore, the wedge-shaped deformed metal occupying the gap is checked based on its appearance.

The present invention is not limited to the embodiments described above, but may be modified into the following examples.

(1) In the first through seventh embodiments, the cylinder head is deformed due to friction welding by a rotary pressing. However, the cylinder head may be deformed due to friction welding by pressing an ultrasonic vibrator. In such a state, the valve seat insert is pressed and vibrated by pressing a vibrating hone thereon.

(2) In the first through seventh embodiments, the cylinder head is made of an aluminum alloy, and the valve seat insert is made of a sintered alloy. However, the cylinder head may be forged iron or cast iron, while the valve seat insert may be a harder metal relative to the cylinder head, including tungsten carbide. In other words, the valve seat insert is harder than the cylinder head, and the material of the cylinder head may be deformed upon pressing the valve seat insert.

(3) In the first through seventh embodiments, the present invention is applied to the valve for an internal combustion engine. However, when a valve repeats opening and closing, and when a valve seat insert is assembled to the end of the port opening of a head, the bonding structure of the valve seat in the embodiments described above may be adopted.

(4) In the first through seventh embodiments, since the valve seat insert is physically secured to the cylinder head, the bonding strength between different metals is not required so much. However, to bond the different metals firmly, and to increase heat conductivity, the valve seat insert, which is made of a sintered alloy, may contain a diffusible material and/or includes a layer of the diffusible material such as copper, zinc, tin and magnesium and alloys of them.

(5) In the third and fourth embodiments, the clearance ε may be set for zero, and the deformed metal flowing onto the outer reduced diameter surfaces <b>42</b>, <b>52</b> may be enclosed. In the seventh embodiment, the cap portion <b>85</b> may be left, and the deformed metal occupying the gap around the inclined surface <b>83</b> may be enclosed. In such a state, the deformed metals occupying the outer reduced diameter surfaces <b>42</b>, <b>52</b>, and the inclined surface <b>83</b> are checked by another way, for example, by nondestructive testing.

According to the present invention described above, the cylinder head is deformed upon pressing the valve seat insert to the head, and the deformed metal occupies the gap around the outer reduced diameter surface of the valve seat insert, then the valve seat insert is physically secured to the head. Thereby, the valve seat insert is firmly bonded, irrespective of a state of bonding between different metals. Also, due to pressure-welding, the valve seat insert may be thinner as compared with those made by heating and press-fitting, and design requirements about dimensions and materials of the valve seat insert may be improved.

According to the present invention, the deformed metal occupying the gap around the outer reduced diameter surface of the valve seat insert is checked based on its appearance. Thereby, quality control about a state of bonding is ensured.

According to the present invention, the deformed metal occupying the gap around the outer reduced diameter surface of the valve seat insert firmly secures the valve seat insert.

According to the present invention, the deformed metal easily occupies the gap around the outer reduced diameter surface of the valve seat insert, and the outer reduced diameter surface filled with the deformed metal is easily checked.

According to the present invention, the deformed metal occupies the gap around the outer reduced diameter surface of the valve seat insert enough.

According to the present invention, initial thrust force upon pressing is reduced.

According to the present invention, the metal deformed upon friction welding secures the valve seat insert to the head.

According to the present invention, applied to the valve seat for an internal combustion engine, design requirements about dimensions and materials of the valve seat insert may be improved, for example, thickness of the valve seat insert may become a relatively thin.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.